1. Field of the Invention
The present invention relates to a high withstand voltage output circuit.
2. Description of the Prior Art
In a high withstand voltage pull-up circuit of used for a display driver, it has hitherto been a practice to use a resistor R as shown in FIG. 1 or a high withstand voltage pnp transistor Tr as shown in FIG. 2 for the constant current source. In the drawings of these figures, Q and D represent a transistor and diode, respectively, at the output stage of individual pull-up circuits to one side a supply voltage HVcc applied and with the opposite side connected to the grounding side (pull-down side).
Both the resistor R of FIG. 1 and transistor Tr of FIG. 2 fail to give the desirable high withstand voltage characteristics since these circuit elements, depending on the supply voltage, will break down. Further, in the circuit of FIG. 1, since the resistor R gives no satisfactory constant current characteristics, the low power consumption and fast response speed are incompatible with each other. In the circuit of FIG. 2 the transistor Tr is slow in response speed and dissipates more power because of leakage to the semiconductor substrate.